4.6 Morphological differentiation of fungal colonies

Changes in the medium of this sort mean that there are consequential changes
in the conditions experienced by hyphae at different positions in the colony and
this results in hyphal differentiation. Hyphal differentiation
is very evident in the morphological differentiation of fungal
colonies (Figs 12 & 13); as nutrients become depleted beneath the
centre of the colony and metabolic products accumulate, spore production is
often initiated.

Fig. 13. Morphological
differentiation of colonies of Aspergillus shown in a photograph
with the peripheral growth zone and other differentiated zones indicated.

Therefore, different parts of the colony are at different
physiological ages, with the youngest actively extending hyphae at
the edge of the fungal colony and the oldest, non-extending, sporulating
mycelium at the centre. This has been demonstrated by estimating variation in
growth rate within a mature colony of Aspergillus niger by measuring
the specific rate of 32P uptake in different zones of the colony
(Table 2).

Table 2. Physiological differentiation in Aspergillus
niger revealed by variation in growth rate within a mature colony
measured by its ability to take up radioactive phosphate.

Uptake of 32P by a mature
colony of Aspergillus niger

Zone of colony (as shown in Fig. 12)

Width of region (mm)

Specific rate of
32P uptake as a percentage of uptake in the peripheral zone